Not Applicable
Not Applicable
The present invention relates to electrically conductive or semi-conductive devices. In particular, this invention relates to electrically conductive or semi-conductive devices comprising an electrically conductive substrate surrounded by a composition comprising an interpolymer of at least one vinyl and/or vinylidene monomer and at least one ethylene and/or -xcex1-olefin monomer. Even more particularly, this invention relates to electrically conductive or semi-conductive devices comprising polymeric insulating or semi-conducting compositions, which have improved electrical properties, service life, and other important properties. The present invention also relates to wires and cables, and ancillary devices, suitable for power transmission or telecommunication.
Typical power cables, including those for small appliances to outdoor station-to-station power cables, often comprise one or more conductors in a core that may be surrounded by one or more layers. These layers may include one or more of the following: a first polymeric semi-conducting shield layer; a polymeric insulating layer; a second polymeric semi-conducting shield layer; and optionally, a metallic tape shield; and a polymeric jacket.
A wide variety of polymeric materials have been utilized as electrical insulating and semi-conducting shield materials for power cables and in other numerous applications. In order to be utilized in services or products where long term performance is desired or required, such polymeric materials, in addition to having suitable dielectric properties, must also be enduring and must substantially retain their initial properties for effective and safe performance over many years of service. For example, polymeric insulation utilized in building wire, electrical motor or machinery power wires, underground power transmitting cables, fiber optic telecommunication cables, and even small electrical appliances must be enduring not only for safety, but also out of economic necessity and practicality. Non-enduring polymeric insulation on building electrical wire or underground transmission cables may result in having to replace such wire or cable frequently.
Common polymeric compositions for use in electrical devices are made from polyvinylchloride (PVC), polyethylene homopolymers, ethylene/vinyl acetate (EVA) copolymer or ethylene-propylene elastomers, otherwise known as ethylene-propylene-rubber (EPR). Each of these polymeric compositions is often undesirable for one or more reasons. For instance, the use and disposal of PVC is often heavily regulated for environmental reasons and a suitable substitute material for use in electrical insulation would be desirable.
Polyethylene is generally used neat without a filler as an electrical insulation material. There have been attempts in the prior art to make polyethylene-based polymers with long term electrical stability. For example, polyethylene has been crosslinked with dicumyl peroxide in order to combine the improved physical performance at high temperature and have the peroxide residue function as an inhibitor of the propagation of electrical charge through the polymer, a process known as tree formation. Unfortunately, these residues are often degraded at most temperatures they would be subjected to in electrical power cable service.
Another class of polymers exists today, and is generally referred to as linear polyethylenes. These types of polymers are described in EPA Publication 0 341 644 published Nov. 15, 1989. Such polyethylenes are produced by a Ziegler-Natta catalyst system and generally have a broad molecular weight distribution similar to linear low density polyethylene and, at low enough polymer density, can also retard tree formation. Such linear type polymers in the wire and cable industry have poor melt temperature characteristics and also must also be cross-linked in order to withstand the high temperatures experienced in wire and cable applications. However, in order to achieve a good mix in an extruder, such linear polymers must be processed at a temperature at which traditionally used peroxides prematurely crosslink the polymers, a phenomenon commonly referred to as xe2x80x9cscorchxe2x80x9d. If the processing temperature is held low enough to avoid scorch, incomplete melting occurs because of the higher melting species in linear polymers with a broad molecular weight distribution. This phenomenon often results in poor mixing, surging extruder pressures, and other poor results.
In contrast to polyethylene, EPR is generally used as an electrical insulator in combination with a high level of filler (typically about 20 to 50 percent by weight). Unfortunately, this combination of EPR and filler usually gives poor dielectric properties.
The use of fillers in combination with substantially random interpolymers for ignition resistant applications is disclosed in a copending U.S. Application by S. R. Betso et al., entitled xe2x80x9cCompositions Having Improved Ignition Resistancexe2x80x9d filed on the same day as the instant application. Also the use of fillers in combination with substantially random interpolymers for use in sound management applications is disclosed in a copending U.S. Application by B. Walther et al., entitled xe2x80x9cInterpolymer Compositions For Use In Sound Managementxe2x80x9d filed on the same day as the instant application. The entire contents of both of these copending applications are incoporated herein by reference
However, a need exists for polymeric insulation having good mechanical and electrical properties and good processability. This invention relates to electrical devices having a polymeric insulating and/or conductive member that exhibit unexpectedly and surprisingly improved electrical and mechanical properties, as well as, good processability.
According to one aspect of the present invention there is provided an electrically conductive device comprising at least one electrically conductive substrate surrounded by a composition comprising at least one substantially random interpolymer comprising:
(i) polymer units derived from
(a) at least one vinyl or vinylidene aromatic monomer; or
(b) at least one hindered aliphatic or cycloaliphatic vinyl or vinylidene monomer; or
(c) a combination of at least one vinyl or vinylidene aromatic monomer and at least one hindered aliphatic or cycloaliphatic vinyl or vinylidene monomer; and
(ii) polymer units derived from at least one aliphatic olefin monomer having from about 2 to about 20 carbon atoms.
According to another aspect of the present invention there is provided an electrically conductive device comprising (a) at least one electrically conductive substrate; and (b) at least one semi-conductive composition in proximity to the electrically conductive substrate. In this aspect, the semi-conducting composition comprises at least one substantially random interpolymer as described above.
According to yet another aspect of the present invention, there is provided an electrically conductive device comprising (a) at least one electrically conductive substrate; (b) at least one semi-conductive composition; and (c) an electrically insulating composition in proximity to the semi-conductive composition. In this aspect, the semi-conductive composition and/or the electrically insulating composition comprise a composition comprising at least one substantially random interpolymer as described above.
According to yet another aspect of the present invention, there is provided an electrically conductive device comprising: (a) at least one electrically conductive substrate; (b) a first semi-conductive composition; (c) an electrically insulating composition in proximity to the first semi-conductive composition and which forms a substrate for a second semi-conductive composition; and (d) a second semi-conductive composition. In this aspect, either semi-conductive member, or both the semi-conductive members, and/or the electrically insulating composition comprise a composition comprising at least one substantially random interpolymer as described above.
According to yet another aspect of the present invention there is provided an electrically conductive device comprising: (a) at least one electrically conductive substrate; and (b) a first semi-conductive composition; (c) an electrically insulating composition in proximity to the first semi-conductive composition and which forms a substrate for the second semi-conductive composition; (d) a second semi-conductive composition; and (e) at least one protective layer. In this aspect, the first and/or the second semi-conductive composition(s) and/or the electrically insulating composition and/or the protective layer comprise a composition comprising at least one substantially random interpolymer as described above.
According to yet another aspect of the present invention there is provided an electrically conductive device comprising: (a) at least one electrically conductive substrate; and (b) at least one protective or insulating layer. In this aspect, the protective or insulating layer comprises a composition comprising at least one substantially random interpolymer as described above.
According to still yet another aspect of the present invention there is provided an electrically conductive device comprising: (a) a plurality of conductors enclosed within a sheath; and interstices between individual conductors and between the conductors and the sheath, wherein the interstices are filled with a composition comprising at least one substantially random interpolymer as described above.